document express customization of fastify endpoint

website/src/pages/docs/integrations/integration-with-fastify.mdx

@@ -79,3 +79,57 @@ app.addContentTypeParser('multipart/form-data', {}, (req, payload, done) =>
 ```
 
 > You can also check a full example on our GitHub repository [here](https://github.com/dotansimha/graphql-yoga/tree/v3/examples/fastify)
+
+## Customize endpoint
+
+By default GraphQL Yoga will expose a `/graphql` endpoint. You can customize it by passing a `graphqlEndpoint` option to `createYoga`:
+
+```ts
+import { createYoga } from 'graphql-yoga'
+import fastify, { FastifyRequest, FastifyReply } from 'fastify'
+
+// This is the fastify instance you have created
+const app = fastify({ logger: true })
+
+const yoga = createYoga<{
+  req: FastifyRequest
+  reply: FastifyReply
+}>({
+  graphqlEndpoint: '/custom/endpoint',
+  // Integrate Fastify logger
+  logging: {
+    debug: (...args) => args.forEach((arg) => app.log.debug(arg)),
+    info: (...args) => args.forEach((arg) => app.log.info(arg)),
+    warn: (...args) => args.forEach((arg) => app.log.warn(arg)),
+    error: (...args) => args.forEach((arg) => app.log.error(arg))
+  }
+})
+
+/**
+ * We pass the incoming HTTP request to GraphQL Yoga
+ * and handle the response using Fastify's `reply` API
+ * Learn more about `reply` https://www.fastify.io/docs/latest/Reply/
+ **/
+app.route({
+  url: '/custom/endpoint',
+  method: ['GET', 'POST', 'OPTIONS'],
+  handler: async (req, reply) => {
+    // Second parameter adds Fastify's `req` and `reply` to the GraphQL Context
+    const response = await yoga.handleNodeRequest(req, {
+      req,
+      reply
+    })
+    response.headers.forEach((value, key) => {
+      reply.header(key, value)
+    })
+
+    reply.status(response.status)
+
+    reply.send(response.body)
+
+    return reply
+  }
+})
+
+app.listen(4000)
+```